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Nickel Metal-Hydride Emulation for Lithium Ion Battery Pack

IP.com Disclosure Number: IPCOM000115982D
Original Publication Date: 1995-Jul-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 104K

Publishing Venue

IBM

Related People

Mito, T: AUTHOR [+2]

Abstract

Disclosed is a technique for applying Lithium Ion (Li-Ion) SMART battery to an Nickel Metal-Hydride (NiMH) battery-powered personal computer system without changing the PC system unit. In other words, NiMH battery pack is emulated by Li-Ion battery. Fig. 1 shows a charge system which implements this invention.

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Nickel Metal-Hydride Emulation for Lithium Ion Battery Pack

      Disclosed is a technique for applying Lithium Ion (Li-Ion)
SMART battery to an Nickel Metal-Hydride (NiMH) battery-powered
personal computer system without changing the PC system unit.  In
other words, NiMH battery pack is emulated by Li-Ion battery.  Fig. 1
shows a charge system which implements this invention.

      It is difficult to apply Li-Ion battery to Nickel NiMH battery
system due to output voltage, discharge profile and charge system.
Recently, some computer systems powered by battery are controlled by
intelligent fuel gauge (SMART) battery system to receive battery data
from battery pack unit.  Battery and IBM ThinkPad 750 incorporates
it.

      Charge: There is no need for NiMH to have constant voltage
power supply but to have Constant Wattage and Constant Current (CWCC)
power supply.  On the other hand, Li-Ion battery requires more severe
voltage tolerance of charge power supply than NiMH.  Usually +/- 1%
is required.  There is no way to control voltage which is applied
from the outside of a battery pack.  Therefore, high conversion
efficiency accurate constant voltage power supply (DC-DC Convertor)
has to be put into the battery pack.  A Diode is provided between (+)
electrode of battery to (+) output of battery pack so that the
current flows reversely.  When the battery pack is empty or needs to
be charged, the fuel gauge will send charge request "04" to "44" to
system unit.  Then, the system unit turns the charge control switch
on.  AC-DC output voltage is applied to Li-Ion battery pack.  This
voltage is converted into accurate voltage to charge the Li-Ion
battery.  When the charge is completed, the fuel gauge sends Full
charge complete data "00" to the system.  Then the system turns off
charge control switch.  There is a system matching problem, when the
charge current is sensed by the fuel gauge circuit; consequently,
emulated voltage data should be +2.4V from emulated voltage data.

      Discharge: Nominal Voltage of NiMH is 1.2V and Li-Ion is 3.6V.
When NiMH is so assembled 7S2P (7 cells in-series 2 parallel), Li-Ion
should be so assembled as 3 cells in-series due to cut-off voltage of
the system unit which will not cause over discharge of Li-Ion battery
pack.  Two cells in-series is not enough fo...